Make causal convolution more robust
Make causal convolution more robust

This rewrites the causal convolution function to handle short small
inputs correctly.

jyegerlehner/tensorflow-wavenet,kutakieu/tensorflow-wavenet,genekogan/tensorflow-wavenet,ibab/tensorflow-wavenet,ibab/tensorflow-wavenet,thakkarV/tensorflow-wavenet,genekogan/tensorflow-wavenet,kutakieu/tensorflow-wavenet,thakkarV/tensorflow-wavenet,jyegerlehner/tensorflow-wavenet